This invention relates generally to devices for dispensing or injecting a fluid at a controlled rate and more particularly to a device for use in the medical field to inject fluids into the body of a patient at a slow rate over a prolonged period of time.
It is desirable in the medical profession to inject fluids such as liquid medicaments into the body of the patient, whether human or animal, at a relatively slow rate over a prolonged period of time. A wide variety of medical treatments require this low rate of injection such as chemotherapy, pre and post surgery treatments for the prevention of blood clotting, various nutrient treatments, various antibiotic treatments and treatment of certain other diseases. Such injections are generally made intravenously or subcutaneously into the patient. Some of these treatments generally require that the fluid be introduced relatively continuously over an extended period of time at a very slow rate, usually in a range varying from less than 1 cc per 24 hour period to move than 5 cc per 24 hour period. Because a significant increase in the predetermined rate of injection during these continuous treatments must be accurately controlled to prevent serious injury or fatality of the patient, the rate of injection must be frequently and closely monitored. Some of these treatments, on the other hand, require that the treatment fluid be injected over a relatively short period of time at a controlled rate in order to gain the peaking benefit of the treatment fluid.
There are a number of liquid dispensing or injection devices presently known which attempt to dispense or inject a liquid into a patient at a very low continuous rate over an extended period of time. A representative sampling of such devices are disclosed in U.S. Pat. Nos. 3,468,308; 3,469,578; 3,486,539; 3,850,348; and 3,868,973. The devices disclosed in these patents rely generally on some pressure producing driving mechanism which constantly tries to force a quantity of liquid into the patient through an appropriate injection device such as a needle. The rate at which the fluid or liquid is injected is controlled by some type of metering device positioned downstream of the container carrying the liquid to be dispensed and through which the liquid to be dispensed must flow before it reaches the patient. One of the problems with such devices is that a failure of the metering device may result in the flow of liquid into the patient being uncontrolled thereby significantly increasing the rate of injection of the fluid into the patient which can result in serious injury or fatality to the patient. Another problem associated with these prior art devices is that because the flow of liquid from the container into the patient is continuous, it is difficult, if not virtually impossible, to accurately and frequently monitor the flow rate of the liquid into the patient. Furthermore, even though the flow rate of the liquid into the patient may be monitored, the complexity of the monitoring technique requires that the patient remain in a confined setting with appropriate qualified medical personnel available to monitor the flow rate. This not only maintains the cost of delivery of the services necessary to dispense or inject the liquid into the patient at a very high level but also seriously limits the patient's ambulatory capability thereby resulting in loss of productive time of the patient. While it is frequently necessary to change the rate of injection of the liquid into the patient during the treatment process, most prior art devices do not have the capability of readily changing the injection rate and/or require that the device be removed from the patient for adjustment or change of injection rate. These prior art devices generally require skilled medical personnel to change the injection rate and also increase the likelihood of infection for the patient.